1. Field of the Invention
This invention relates to a coloring device which can compress image data and generate a color image from a monochromatic photograph by automatically generating a color graphic form or image from a monochromatic graphic form or image when a color image is generated from a monochromatic image and which can be applied to, for example, a color image storage device and a color facsimile system.
2. Description of the Related Art
Previously, three-primary-color signals have been considered as variables or variates independent of each other. Thus, there have been made few researches on compression and coding of color image data using the correlations among the three primary colors. However, several researches have been carried out recently on reproduction of a color image from a monochromatic image using local correlations among color images. For the particulars of such researches, please refer to, for example, an article entitled "Prediction and Reproduction of Color Image from Monochromatic Image Using Correlations among Three Color Signals" written by Kodera et al., Proceedings of '88 National Conference of Institute of Electronics and Communication Engineers of Japan.
Hereinafter, this conventional system will be explained by referring to FIG. 4. In this figure, reference numerals 41, 42 and 43 indicate data on the three primary colors (red; green; and blue, or cyan; magenta; and yellow) of color images. Let 42 denote data on a reference color. With respect to data of a block composed of n.times.m picture elements or pixels (FIG. 4 shows the case where the block is composed of 3.times.3 pixels), prediction coefficients relating to the color data 41 and 43 of predetermined polynomials are respectively evaluated in the prediction coefficient evaluating portions 50 and 51 on the basis of the data on the reference color. The data on the reference color and the prediction coefficients of each block are then sent to the next stage. Thereafter, prediction is effected with regard to each block from the data 41 and 43 by prediction portions 52 and 53 by using prediction functions, and thus data 49 and 50 are reproduced.
In the prior art, an adaptive prediction function can be obtained for each block of pixels, though the form of the function is limited to a predetermined polynomial. Thus, the prior art coloring devices have not employed approximation by using nonlinear combination of polynomials. This results in that the prior art coloring devices have encountered a problem that the approximation cannot be optimized in some images.
The present invention is provided to eliminate the drawbacks of the conventional system.
It is therefore an object of the present invention to provide a coloring device which can generate an optimized color image by adaptively coloring a monochromatic image.